Scala error handling: Try or Either? -

given method in userservice: update, what's best way handle errors/exceptions here?

option a:

def update(...): try[user] 

in way, need define custom exceptions , throw them in function body while needed. of these exceptions business errors (e.g. user_id cannot changed, etc). point here no matter exception(s) thrown (business error, network exception, db io exception, etc), threat them same , return failure(err) - let upper layer handle them.

option b:

def update(...): either[error, user] 

this exception-free way. in function body catches possible exceptions , turns them error, , business errors return left[error].

using try seems more natural way me want handle errors. either more generic thing - either[error, t] 1 special case , think try invented special case. read should avoid using exceptions error handling...

so, solution better, , why?

there's no silver bullet.

as noted already, try more specialized version of either, left type fixed throwable.

try might fit if need materialize exceptions thrown external (perhaps java) libraries, constructor automatically catches them.

another advantage of try has map , flatmap, can use directly in for-comprehensions, whereas either have explicitly project on right case. anyway, there's plenty of alternative implementations "right-bias", , scalaz \/ type popular one.

that being said, typically use \/ or equivalent validation (both scalaz), having ability of returning errors not extend throwable.

it allows more precise error types, huge win.